Can "I have" be contracted when talking about possession?

Hello everyone. I've recently seen some people contracting "I have" into "i've" when indicating possession and it doesn't sound right at all to me. I don't remember whether or not this is actually acceptable, or maybe more common in British English. Can anyone help?

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It's less common but it is used that way sometimes, I've done it myself, but it does look a little weird sometimes when you come across it while reading. It might be more common for the Brits. I'd recommend non-natives avoid it.
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The reduced form is more informal.
When speaking about possessions, this should be followed by GOT (I've got). That seems to be a regular pattern observed across the globe.
Hi Redseahorse, thank you for your answer.

I am already familiar with the "I've got" structure. What I was referring to is this:

I've two children.
I've an IPhone.

Etc... Is it actually normal at all or were the people saying it like that making a mistake?